///
// * jdbm LICENSE v1.00
// *
// * Redistribution and use of this software and associated documentation
// * ("Software"), with or without modification, are permitted provided
// * that the following conditions are met:
// *
// * 1. Redistributions of source code must retain copyright
// *    statements and notices.  Redistributions must also contain a
// *    copy of this document.
// *
// * 2. Redistributions in binary form must reproduce the
// *    above copyright notice, this list of conditions and the
// *    following disclaimer in the documentation and/or other
// *    materials provided with the distribution.
// *
// * 3. The name "jdbm" must not be used to endorse or promote
// *    products derived from this Software without prior written
// *    permission of Cees de Groot.  For written permission,
// *    please contact cg@cdegroot.com.
// *
// * 4. Products derived from this Software may not be called "jdbm"
// *    nor may "jdbm" appear in their names without prior written
// *    permission of Cees de Groot. 
// *
// * 5. Due credit should be given to the jdbm Project
// *    (http://jdbm.sourceforge.net/).
// *
// * THIS SOFTWARE IS PROVIDED BY THE ndbm PROJECT AND CONTRIBUTORS
// * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
// * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
// * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
// * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
// * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
// * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
// * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
// * OF THE POSSIBILITY OF SUCH DAMAGE.
// *
// * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
// * Contributions are Copyright (C) 2000 by their associated contributors.
// *
// * $Id: FreePhysicalRowIdPage.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
// 

//*************************************************************************
//**  Included in JDMB 1.0 port to SharpDBM;  11/2013 Cyrus Neah cneah@codingreal.com
//**  SharpDBM is an independent reimplementation of the JDBM 1.0 software library in C#  
//*************************************************************************

namespace SharpDBM.recman
{

///
// *  Class describing a page that holds physical rowids that were freed.
// 
	public   class FreePhysicalRowIdPage : PageHeader
	{
	// offsets
		private const short O_COUNT = PageHeader.SIZE; // short count
		internal const short O_FREE = O_COUNT + Magic.SZ_SHORT;
		internal const short ELEMS_PER_PAGE = (RecordFile.BLOCK_SIZE - O_FREE) / FreePhysicalRowId.SIZE;

	// slots we returned.
		internal FreePhysicalRowId[] slots = new FreePhysicalRowId[ELEMS_PER_PAGE];

//    *
//     *  Constructs a data page view from the indicated block.
//     
        public FreePhysicalRowIdPage(BlockIo block)
            : base(block)
		{
		}

//    *
//     *  Factory method to create or return a data page for the
//     *  indicated block.
//     
		public static FreePhysicalRowIdPage getFreePhysicalRowIdPageView(BlockIo block)
		{
	  BlockView view = block.getView();
	  if (view != null && view is FreePhysicalRowIdPage)
		  return (FreePhysicalRowIdPage) view;
	  else
		  return new FreePhysicalRowIdPage(block);
		}

	/// Returns the number of free rowids 
		internal virtual short getCount()
		{
	  return block.readShort(O_COUNT);
		}

	/// Sets the number of free rowids 
		private void setCount(short i)
		{
	  block.writeShort(O_COUNT, i);
		}

	/// Frees a slot 
		internal virtual void free(int slot)
		{
	  @get(slot).setSize(0);
	  setCount((short)(getCount() - 1));
		}

	/// Allocates a slot 
		internal virtual FreePhysicalRowId alloc(int slot)
		{
	  setCount((short)(getCount() + 1));
	  return @get(slot);
		}

	/// Returns true if a slot is allocated 
		internal virtual bool isAllocated(int slot)
		{
	  return @get(slot).getSize() != 0;
		}

	/// Returns true if a slot is free 
		internal virtual bool isFree(int slot)
		{
	  return !isAllocated(slot);
		}


	/// Returns the value of the indicated slot 
		internal virtual FreePhysicalRowId @get(int slot)
		{
	  if (slots[slot] == null)
		  slots[slot] = new FreePhysicalRowId(block, slotToOffset(slot));
		  ;
	  return slots[slot];
		}

	/// Converts slot to offset 
		internal virtual short slotToOffset(int slot)
		{
	  return (short)(O_FREE + (slot * FreePhysicalRowId.SIZE));
		}

//    *
//     *  Returns first free slot, -1 if no slots are available
//     
		internal virtual int getFirstFree()
		{
	  for (int i = 0; i < ELEMS_PER_PAGE; i++)
	  {
		  if (isFree(i))
		return i;
	  }
	  return -1;
		}

//    *
//     *  Returns first slot with available size >= indicated size,  
//     *  or -1 if no slots are available.
//     *
		internal virtual int getFirstLargerThan(int size)
		{
	  for (int i = 0; i < ELEMS_PER_PAGE; i++)
	  {
		  if (isAllocated(i) && @get(i).getSize() >= size)
		return i;
	  }
	  return -1;
		}
	}

}